Detergents and other treatment agents to be applied in foamy condition to a moving substrate of significant width, e.g. 5 m and more, are difficult to apply with the uniformity usually desired. Such uniformity is especially hard to maintain when only a thin layer of the treatment agent is to be spread over the surface of the substrate even as the consistency and other properties of the foam are to be preserved up to the point of its deposition, to be followed by its subsequent dissolution without traces. Thus, conventional wisdom dictates that the liquid foam ought to be applied as soon as possible after it has been generated, in order to prevent any intervening deterioration.
It is therefore customary to juxtapose the applicator closely with the foam generator; this, however, impedes the desired uniformization since the usual foaming devices respond but slowly to corrective signals indicating a deviation of the dispensed foam from an established norm.